1. Field of the Invention
The present invention relates generally to hydraulic valves and actuator assemblies. More particularly, the present invention relates to a hydraulic valve and actuator assembly that includes an outwardly opening, seat-sealed, force balanced needle valve.
2. Description of Related Art
Improved energy efficiency and pressure control responsiveness have been demonstrated in advanced diesel fuel injection systems that utilize cyclic energy storage and recovery operating principles. One benefit of an outwardly opening valve is that the pressurized fluid can maintain (or hydraulically latch) the valve in a closed state during an energy storage cycle after only a brief actuation to close the valve. Hydraulic latching allows externally supplied actuation energy to be conserved and for valve reopening to be passively synchronized with the conclusion of the energy recovery cycle and the beginning of the refilling cycle. A benefit of a seat-sealed valve is that parasitic leaks are virtually eliminated. Eliminating parasitic leaks improves energy efficiency, power density, and performance. A disadvantage of the outwardly opening feature is that an excessive pressure drop can develop across the valve during a spill cycle that encourages premature closing (or blow-shut). A blow-shut may result in greater than desired operating pressures. Conventional approaches to address this problem include increasing the strength of the spring that holds the valve in an open position and utilizing a change of flow momentum to counteract the blow-shut problem. The systems that increase the strength of the spring increase not only the size and cost of the spring, but also the size and cost of the actuator because the actuator must be able to overcome the spring to close the valve and to keep the valve closed. The systems that utilize a change in flow momentum incur substantial flow loss penalties.
Conventional valve assemblies have relied upon the de-energization of a valve actuator to open the valve. The timing of this opening with the pump has caused problems, in that the valve may be opened prematurely, in which case the energy expended to increase the pressure in the pump is lost into the supply, or the valve may be opened too late, in which case the pump expends energy in creating a vacuum in the pump chamber and may even reduce the pressure of the system being supplied by the pump. Additional sensing and control elements can be considered to minimize or eliminate these problems at the expense of additional cost, complexity, and unreliability.
An exemplary embodiment of the invention coordinates the flow restrictions and accompanying pressure differentials through the valve assembly with the surface areas upon which those pressures act to control the forces operating on the valve. An exemplary embodiment of the invention provides an outwardly opening, seat-sealed and force balanced valve. The exemplary embodiment of the invention performs at least one of the following functions of eliminating premature closing or blow-shut; reducing actuator force; controlling logic and electrical requirements; increasing the minimum flow cross-section; reducing the package size; and supporting advanced valve motion diagnostics using electromagnetic force feedback.
An exemplary embodiment of the invention enables the valve actuator to be de-energized while the pump is increasing the pressure by relying upon the hydraulic latching of the valve in a closed position. Since, the actuator is de-energized, as soon as the pump piston reduces the pressure in the pump chamber to a pressure that is lower than the supply pressure, the valve opens by itself.
The exemplary embodiment of the invention reduces the spring strength that is required to maintain the valve in an open configuration by controlling the forces exerted on a movable valve element such that the movable valve element is biased open during a spilling mode. Since the strength of the spring biasing the valve open may be reduced, the strength of the actuator of the exemplary embodiment may also be reduced. Therefore, a smaller and more compact actuator, spring and overall valve package size may be obtained for a given flow handling capacity on a cycle by cycle basis.
While preserving the advantages of an outwardly opening valve, an exemplary embodiment of the invention provides a more nearly balanced application of fluid forces on the valve element, while in its open position, to help prevent premature closing or latching of the valve. Accordingly, an exemplary embodiment of the invention finds particular utility in diesel fuel systems that utilize cyclic energy storage and recovery.
Additionally, low actuation force requirements permit electro-magnetic actuators to be operated without magnetic saturation, thereby allowing the coil assembly of the actuator to be used to sense the position of the movable valve assembly within the valve body. The coil assembly may therefore be used to generate a signal that may be used in advanced valve motion diagnostics using electromagnetic force feedback.
An exemplary embodiment of the present invention maximizes the flow capacity of the valve while simultaneously reducing the pressure drop through the valve and, thereby, improves the efficiency of the valve. The movable valve assembly of the present invention is also designed such that the surface areas exposed to the fluid pressures within the valve body operate to balance the forces upon the movable valve assembly. The pressures within the valve body which operate upon the surface areas of the movable valve assembly are controlled based upon the flow of the fluid upstream through the valve and upon the restrictions through which the fluid flows. The restrictions to flow may be reduced by increasing the surface area of the movable valve assembly exposed to the pressures within the valve body. In this manner, the upstream flow restrictions may be reduced.
In an exemplary embodiment of the invention a first chamber is formed above a radially extending portion of a movable valve element and a predetermined flow restriction is formed upstream of the first chamber which is more restrictive than the flow restriction formed between the radially extending portion of the movable valve element and the adjacent valve seat. Thus, when the valve is in its open position and the flow of fluid through the valve reverses (in a spilling mode), the pressure in the first chamber will tend to increase to tend to maintain the valve element in its open position. An internal passage within the movable valve element places the first chamber in fluid communication with a second chamber above the movable valve element to add further force tending to hold the valve element open during reverse flow of fluid through the valve.